These telescopes are equipped with CCD detectors operating in the visible range and are cooled to a low temperature (0.degree. to 5.degree. C.) in a space whose temperature is controlled by a thermostat.
During the pointing time, these detectors are subjected to attacks of nuclear radiation. The CCD components are formed from semiconductor materials, whose parameters are degraded when the detector is struck by a bombardment of particles. This happen because at a constant temperature the dark current increases. Since this current decreases with temperature, it is necessary to overcool or cool when this current has increased in order to re-establish the increased current to its desired value in the absence of nuclear attack and thus to maintain the initial sensitivity of the detector.